The present invention relates to a process for preparing carbene-ruthenium complexes and also novel arylalkylidene-ruthenium complexes which can be prepared on the basis of this process and can be used, for example, as catalysts in metathesis reactions.
Increasing efforts have been made in recent years to prepare homogeneous catalysts which are both thermally stable and stable to water and air for olefin metathesis. Specific ruthenium-alkylidene compounds have attracted particular interest here.
Carbene-ruthenium complexes are extremely effective catalysts for olefin metathesis. Their unique properties, e.g. the high tolerance to water, air and polar functional groups, is the reason why they are used in organic synthesis to an ever increasing extent. The greatly increased demand and the manifold possible uses of these catalysts have inevitably led to a search for alternative synthetic routes.
Ruthenium metal-carbene complexes of the general structure RuX2(═CH—CH═CR2)L2 for the metathesis polymerization of olefins are described, for example, in the patent applications WO 93/20111. Triphenylphosphane and substituted triphenylphosphane are used as ligands L. The complexes are prepared by reaction of RuCl2(PPh3)3 with suitable disubstituted cyclopropenes as carbene precursors.
However, the cyclopropenes are thermally unstable and are not commercially available. For this reason, they have to be prepared in a complicated process shortly before the synthesis.
Similar reactions with [Ru(p-cymene)Cl]2 are described in WO 96/04289.
WO 97/06185 likewise describes metathesis catalysts based on ruthenium metal-carbene complexes. They can be prepared by reaction of RuCl2(PPh3)3 with diazoalkanes.
However, handling diazoalkanes represents a safety risk, especially when carrying out the process on an industrial scale.
Hill et al. Dalton 1999, 285-291, describe the synthesis of Ru-indenylidene complexes from RuCl2(PPh3)3 and diphenyl-propargyl alcohol.
Hoffmann et al. Journal of Organometallic Chemistry 641 (2002) 220-226, describe the synthesis of Ru-alkylidene complexes from the Wilkinson hydride complex RuHCl (PPh3)3.
For both processes, the organometallic starting material of the formula RuCl2(PPh3)3 which is used has to be prepared from RuCl3 using a large excess of triphenylphosphane (PPh3). However, in the catalyst synthesis itself, PPh3 ligands are lost again after the ligand exchange.
Grünwald et al. [Grünwald, C., Gevert, O., Wolf, J., Gonzàlez-Herrero, P., Werner, H., Organometallics 15 (1996), 1969-1962] describe a process for preparing ruthenium complexes in which polymeric [RuCl2(COD)]n is reacted with hydrogen in i-propanol in the presence of phosphane.
These processes have the disadvantage that long reaction times and a two-fold excess of phosphane are required.
According to a method described in EP0839821, the reaction proceeds without hydrogen and less phosphane is needed. However, vinylidene complexes are often formed in this method of carrying out the reaction, as described, for example, by Ozawa [H. Katayama, F. Ozawa Organometallics 17 (1998), 5190-6 ].
WO 9821214 describes syntheses of carbene complexes which start out from the ruthenium polyhydride RuHCl (H2)x(PCy3)2, where PCy3 is tricyclohexylphosphane.
However, the ruthenium polyhydride complex is difficult to obtain. In addition, long reaction times are required.
The known synthetic routes for preparing metathesis catalysts of the type RuX2(═CH—R) (PR′3)2 are uneconomical for the stated reasons.
The patent DE19854869 describes a one-pot synthesis of the carbene-ruthenium complexes RuX2(═CH—CH2R) (PCy3)2 from RuCl3, Mg, PCy3, hydrogen and acetylene.
However, handling acetylene represents a safety risk, particularly when carrying out the process on an industrial scale.